STUDIES OF THE PINK BOLLWORM IN MEXICO 
63 
The differences here are so slight that the effectiveness of all the 
poisons must be considered about the same. In the records for 1921 
(Table 48, plats 2, 4, 6, and 8) the effectiveness of calcium arsenate 
and that of arsenite of zinc compare in a similar wav. 
ACTION OF THE POISON ON THE PINK BOLLWOEM 
In the fall of 1922 experiments were begun to determine the manner 
in which the application of arsenicals to cotton reduces the pink boll- 
worm infestation. It was planned to determine by applications of 
dust, in one case to the entire plant except the bolls, and in another 
to the bolls only, whether the young larvae are killed while they feed on 
the foliage or while they attempt to enter the boll. A few plants 
were selected for each test and young bolls on them labeled, including 
bolls on separate plants to serve as checks. Applications of dust 
were made every five days and repeated after rains. An exami- 
nation of50 small bolls as a check at the beginning of the experiment 
showed ah average of 0.38 worm per boll. The results of this experi- 
ment are summarized in Table 51. 
Table 51. — Effect on pink bollworm infestation of the application of calcium 
arsenate dust on bolls only and on the rest of the plant only 
Period of treat- 
ment 
Num- 
ber of 
bolls 
Eggs and eggshells 
on bolls 
Larvae and 
exit holes 
Dead 
Part of plant dusted 
Total 
eggs 
Total 
egg- 
shells 
Aver- 
age 
per 
boll 
Total 
Per 
boll 
larvae 
in 
bolls 
Entire plant except bolls 
Check 
Sept. Ito30 
100 
82 
SO 
58 
3 
46 
4 
55 
96 
227 
30 
242 
0.99 
3.33 
.68 
5.12 
209 
277 
185 
2Sfi 
2.09 
3.38 
13 
17 
Bolls only 
Check 
Sept. 1 to Oct. 3— 
None 
3.70 j 6 
4.41 ' 9 
Average, both checks 
4.07 - 
3.80 
Keduction in infestation was brought about in both cases, but it 
was more marked where the foliage was dusted than where the bolls 
only were dusted. It would appear that young larvae were killed 
both while feeding on the foliage of dusted plants and while entering 
the bolls. But the most striking point in the results is the great 
reduction in the number of eggs found on the bolls after dusting. 
This was found to be the case also in the examination of bolls from 
plats in the other poison tests. It suggests that the reduction in 
infestation may not have been brought about at all by killing of the 
larvae, but by repelling the moths. This point should be closely 
studied in connection with further dusting experiments. 
SUMMARY 
An average annual loss of from 20 to 25 per cent of the cotton 
crop has been caused by the pink bollworm in Mexico, since the 
infestation attained maximum development. There is a reduction 
in both the quantity of the total crop picked and the quality of the 
lint and seed marketed. 
